From inside (document excerpt):

Instruction Manual EJ-41U Terminal Node Controller Unit Thank you for purchasing this fine Alinco product. This unit enables data communication when it is properly installed in designated Alinco transceivers. Please read this manual, print the contents if necessary, and keep this disk for future reference. Since this device is capable of being used in commercial applications, some of the pages in this manual are intentionally left blank to accommodate those uses in other regions.

Although we attempt to explain the features of this unit in a simple and comprehensive manner, unless you have some knowledge about packet communications and APRS, you may have difficulty understanding the contents of this manual. We apologize, but Alinco cannot provide basic information of how packet and/or APRS works in general. Please consult your favorite Ham radio stores for books on the subject and/or web-sites that support your area of interest regarding those communication modes. You can explore the exciting world of data communication by yourself, and we believe that this is a most interesting part of the king of hobbies, Amateur Radio. APRS® is a registered trademark of Bob Bruninga, WB4APR Notice · This unit should be used with ALINCO transceiver DR-135T/E. · The memory of all settings of the unit are retained by the built-in lithium battery. If they go back to the default, the battery might be consumed. In that case consult the dealer. Accessories The accessories listed below are included. Check that all of them are found before using. · EJ-41U · 3.5ø stereo plug (for GPS input terminal) · Velcro for installation · Instruction Manual · Instruction Manual DISK version Installation 1) Remove the bottom case of DR-135. 2) Attach Velcro on the VCO case. 3) Unplug W1 of DSUB-9 connector from CN107 and plug it into CN1 connector of EJ-41U. 4) Plug W2 of EJ-41U to the transceiver connector CN107. 5) Attach Velcro on EJ-41U so that it matches to the other Velcro on the VCO case.